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Observation Constraints of the End of Reionization

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Gemini Keck. From Avi Loeb. reionization. Two Key Constraints: WMAP 3-yr: zreion=10 /-3 ... 0.6 (2-sigma) by fitting both DLA and IGM profiles. Damping wing? ... – PowerPoint PPT presentation

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Title: Observation Constraints of the End of Reionization


1
Observation Constraints of the End of
Reionization
  • Xiaohui Fan
  • University of Arizona

Collaborators Becker, Carilli, Ferrara,
Gallerani, Jiang, Richards, Roy Choudhury,
Strauss, Xu, Walter, White, et al.
Background 46,420 Quasars from the SDSS Data
Release Three
2
The Highest Redshift Quasars Today
  • z4 1000 known
  • z6 19
  • SDSS i-dropout Survey
  • Completed in June 2006
  • 7700 deg2, zAB
  • 27 luminous quasars at 5.71
  • CFHT High-z Quasar Survey (CFHTQS, Willott et al.
    astro-ph/0706091)
  • Goal 400 deg2, zAB
  • 4 quasars at z6
  • New highest-z quasar at z6.43
  • SDSS Faint Quasar Survey (SFQS)
  • faint quasars in the deep SDSS stripe (Jiang, XF
    et al.),
  • 300 deg2, zAB
  • six z6 quasar at 20
  • Goal quasar LF
  • Other on-going z6 quasar surveys
  • AGES (Cool et al.) Spitzer selected, one quasar
    at z5.8
  • FIRST-Bootes (Becker et al.) radio selected, one
    quasar at z6.1
  • QUEST i-dropout surveys similar to SDSS
  • IR-based survey UKIDSS, (z5.83), VISTA, allows
    detection up to z8-9.


3
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4
Quasar Density at z6
  • From SDSS i-dropout survey
  • Density declines by a factor of 40 from between
    z2.5 and z6
  • Cosmological implication
  • MBH109-10 Msun
  • Mhalo 1012-13 Msun
  • rare, 5-6 sigma peaks at z6 (density of 1 per
    Gpc3)
  • Assembly of supermassive BHs?
  • The universe is only 20 teddington old,
    requiring non-stop Eddington accretion of 100
    Msun from z20
  • Is Eddington-limited accrection from stellar
    seeds still permitted, or are alternative
    accretion modes (super-Eddington, intermediate
    mass BH) needed?

Fan et al. 2006
5

The Lack of Evolution in Quasar Emission Line
Properties

z6 composite
Ly a
Low-z composite
NV
OI
SiIV
Ly a forest
Fan et al.2007
  • Rapid chemical enrichment in quasar vicinity
  • Quasar env has supersolar metallicity no
    metallicity evolution
  • High-z quasars are old, not yet first quasars..

6
Quasar Metallicity at z6
near-IR spectroscopy Gemini Keck
Jiang, XF et al. 2007
7
reionization
  • Two Key Constraints
  • WMAP 3-yr zreion10/-3
  • 2. IGM transmission zreion 6

From Avi Loeb
8
End of Reionization EpochOpen Questions
  • Whats the Status of IGM at z6?
  • Measurements of Gunn-Peterson optical depth
  • Evolution of UV background
  • Constraints on IGM neutral fraction
  • Was the Universe mostly neutral by z6-8?
  • Distribution of dark gaps
  • HII region size distribution
  • Evolution of Lyman alpha emitters
  • What is the source of reionization?
  • First galaxies or AGNs

9
Searching for Gunn-Peterson Trough
  • Gunn and Peterson (1965)
  • It is observed that the continuum of the source
    continues to the blue of Ly-a ( in quasar 3C9,
    z2.01)
  • only about one part of 5x106 of the total mass
    at that time could have been in the form of
    intergalactic neutral hydrogen
  • Absence of G-P trough ? the universe is still
    highly ionized at z6

10
Keck/ESI 30min exposure ?
Gunn-Peterson Trough in z6.28 Quasar
Keck/ESI 10 hour exposure ?
White et al. 2003
11
Evolution of Lyman Absorptions at z5-6
?z 0.15
12
Accelerated Evolution at z5.7
  • Optical depth evolution accelerated
  • z
  • z5.7 ? (1z)11
  • End of reionization?
  • Dispersion of optical depth also increased
  • Some line of sight have dark troughs as early as
    z5.7
  • But detectable flux in 50 case at z6
  • End of reionization is not uniform, but with
    large scatter

(1z)11
(1z)4.5
XF et al. 2006
13
Evolution of Ionization State
UV background
  • UV Ionizing background
  • Assuming photoionization and model of IGM density
    distribution
  • UV background declines by close to an order of
    magnitude from z5 to 6.2
  • Increased dispersion suggests a highly
    non-uniform UV background at z5.8

Neutral fraction
  • From GP optical depth measurement, volume
    averaged neutral fraction increase by order of
    magnitude from z5.5 to 6.2

XF et al. 2006
14
Relation between optical depth and neutral
fraction highly model-dependent
  • Becker et al. (2006)
  • optical depth evolution could be consistent with
    a smooth evolution of ionizing background for a
    strongly-evolving log-normal density distribution
    of the IGM
  • Relation between ? and ? dependent on IGM
    clumpiness
  • Simulation results clumpiness 5 - 30, no
    strong evolution at z6
  • Optical depth evolution driven by an decreasing
    background towards high-z

Becker et al. 2006
15
Evolution of Proximity Zone Size Around Quasars
Shapiro, Haiman, Mesinger, Wyithe, Loeb et al.
  • Size of Proximity Zone region
  • Rp (LQ tQ / fHI )1/3
  • Size of quasar proximity zone decreases by a
    factor of 2.4 between z5.8 and 6.4 (Fan et al.
    2006)
  • Consistent with neutral fraction increased by a
    factor of 15 over this narrow redshift range
  • Can be applied to higher z and fHI with lower S/N
    data
  • Actual size of proximity zone dependent on
    details of radiative transfer and quasar model

Proximity zone size (Mpc)
XF et al. 2006
redshift
16
Uncertainties in interpretation of proximity zone
sizes
  • Bolton Haehnelt (2006), Maselli et al. (2006)
  • Observed size of proximity zone much smaller than
    true HII region size
  • Neutral fraction
  • Consistent with G-P constraints
  • Mesinger et al. (2004), Wyithe et al. (2005)
  • Neutral fraction 10-30
  • Better models and simulated spectra needed

Maselli et al. 2006
Bolton Haehelt 2006
17
CFHTQS results (Willott et al. 2007)
  • Strong evolution in ?GP seen at z5.5, but low
    S/N
  • Scaled near-zone size 6-11 Mpc at z6
  • Consistent with a low fHI
  • But uncertainties in zem based on Ly?
  • Caution using Ly? redshift could introduce large
    uncertainty in HII region size but true
    systematic redshift difficult for faint quasars
    at z6

18
Dark Gap Distributions
  • Dark gap statistics (Songaila Cowie 2002)
  • Gaps regions where all pixels have ?2.5
  • Gaps among z6 quasars
  • Average length shows the most dramatic increase
    at z5.8 ? IGM is dominated by long, dark gaps
  • Consistent with overlap at z6-8?
  • Dispersions
  • Even at z6, gap lengths are still finite
  • Upper limit on neutral fraction
  • If IGM largely neutral, GP damping wing will wipe
    out all HII region transmissions
  • Existence of transmission at z6 places an upper
    limit of average neutral fraction
    et al. 2007)
  • Independent upper limit on neutral fraction

XF et al. 2006
19
Dark Gap Statistics Comparison with Simulations
  • Gallerani et al. (2006, 2007)
  • Early reionization (zoverlap 15)
  • Late reionization (zoverlap 7)
  • Significant difference in gap distribution at z6
  • fHI
  • But observed transmission peaks too wide compared
    to simulations

Distribution of width of transmission peaks
Distribution of dark gaps
5.7
6.0
20
Ly ? Galaxy LF at z6
Iye et al. 2006 Kashikawa et al. 2006
  • Neutral IGM has extended GP damping wing ?
    attenuates Ly ? emission line
  • New Subaru results
  • Declining density at z6-7 (2-3? result)
  • Reionization not completed by z6.5
  • Neutral fraction could be as high as a few tenths
    but strongly model-dependent
  • cf. Malhotra Rhoads, Hu et al. lack of
    evolution in Ly ? galaxy density

21
GRBs as Probes of Reionization
Damping wing?
GRB050904
  • Detected to z6.30
  • Advantages
  • Bright
  • Flat K-correction due to time dilation at high-z
  • Small surrounding HII regions could use damping
    wing of Gunn-Peterson trough to probe high
    neutral fraction
  • Constraining neutral fraction
  • How to distinguish internal absorption from IGM
    damping wing??
  • Using 050904 fHI DLA and IGM profiles

Kawai et al. 2005
22
What Ionized the Universe? AGNs or Galaxies
Density of quasars
SFR of galaxies
  • Quasar LF at z6
  • SDSS Wide 7700 deg2, 17 quasars, zAB
  • SDSS Deep 150 deg2, 6 quasars, 20
  • AGES 1 quasar in 5 deg2 at zAB
  • Steeppening of LF
  • ??L-3.1
  • Comparing to ??L-2.4 at z4

Jiang, XF et al. 2007
23
Reionization by AGNs?
  • Can quasars do it?
  • Too few quasars unless QLF remains to be steep to
    AGN luminosity
  • Can low-luminosity AGNs ionize the IGM by z6?
  • Stacking X-ray image of LBGs in UDF too few
    faint AGNs
  • Can accretion to seed BHs ionize the IGM by z15?
  • Dijkstra, Haiman Loeb (2004)
  • Soft X-ray background overproduced if quasars
    produce 10 photons/H atom
  • Preionization to f(HI)50 by X-rays is still
    allowed (e.g. Ricotti et al.)

Jiang, XF et al. 2007
24
Summary
  • IGM evolution accelerated at z6
  • Neutral fraction increased by order of mag from
    z5.5 to z6
  • fHI a few percent, but highly model-dependent
  • z6 marks the end of overlapping stage of an
    inhomogeneous reionization
  • z6 quasars are old lots of BH build-up and
    chemical enrichment at high-z
  • AGN not likely sources of reionization

25
Probing Reionization History

WMAP
26
Surveys of quasars at z7
LBT LBC-Red i-z-Y selection (1 deg2/night)
UKIDSS YJHK photometry
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